In many instances, there is a need to fasten two objects together so that they can be subsequently separated without destruction of either of the objects. This problem has been solved imperfectly by the use of threaded fasteners. There are many threaded fasteners which have a self-locking feature, but there are none with the degree of reliability which results from a riveted or welded connection between objects. It has been a long sought after goal to provide a threaded fastener which will operate with the reliability of a riveted or welded connection. This need for reliability is particularly acute where assembled objects operate at high temperatures. Typical high temperature applications such as engines and turbines are ones in which assembled parts are heated during operation of the engine or turbine and then cooled when the engine or turbine is not operating. This temperature cycling produces severe expansion and contraction of a threaded fastener. The cyclical expansion and contraction takes a toll on fastener reliability.
Many prior art self-locking threaded fasteners rely on elastomeric inserts as locking devices. These fasteners are unsuitable for high temperature applications, i.e., temperatures above 200 degrees centigrade. When these fasteners are exposed to high temperatures such as those encountered in a turbine, the elastomeric inserts are useless because they disintegrate.
Another problem that develops with threaded fasteners in high temperature settings is corrosion. Typically, the fastener is made from a material that is dissimilar to the objects being held together. Virtually any dissimilarity between adjacent metal at high temperature will result in corrosion. When a threaded fastener corrodes, it loses some of its strength. Corrosion of a fastener also creates an undesirable adhesion between the threads of the fastener and the objects being fastened. Consequently, when the time comes to disassemble the secured objects, it is often the case that the fastener will not unthread from the object but will instead break away inside the object.
It is desirable therefore to provide a self-locking fastener that is highly reliable when securing objects at a high temperature but will be readily releasable when the objects are at a low temperature. It is also desirable that such a fastener can be produced in an expedient and cost effective manner.